However, the party’s lawyers reject the accusation, and claim that the track used in the TV advertisement campaigning for then-leader John Key’s re-election was not actually Lose Yourself, but a tune purchased from a stock music library.

The hearing began in Wellington on Monday (May 1), with both tracks played in court.

Gary Williams, a lawyer for Eminem’s music publishers Eight Mile Style, stated that the National Party infringed copyright by using the tune, or a substantial reproduction of it, even though the song’s lyrics weren’t used in the ad.

“The song ‘Lose Yourself,’ is without doubt the jewel in the crown of Eminem’s musical work,” Williams said, in his opening statements to the court, according to The New Zealand Herald.

“The licensing of the song has been extremely carefully controlled. Despite many requests, it has only rarely been licensed for advertising purposes.”

During his statement, Williams also quoted from National Party emails, including one in which the tune is described as an Eminem “sound-alike”. He went on to claim the email showed it was “utterly clear” the party knew it was using a copyrighted song.

The backing track had been taken from a library made by Australian production music company Beatbox, and the National Party denies being responsible for any alleged copyright infringement.

Lawyer for the National Party, Greg Arthur, said that the “clear position” of the political party was to make sure there would be no possibility of copyright infringement.